Method and system for enhancing efficiency by modulating power amplifier gain

ABSTRACT

Aspects of a method and system for enhancing efficiency by modulating power amplifier (PA) gain are presented. Aspects of the system may comprise a PA gain modulator that enables modification of an amplitude of a digital baseband signal. A baseband processor may enable computation of a first gain value based on the modification. The baseband processor may enable computation of a second gain value based on the first gain value. A PA may enable generation of an RF output signal based on the modified digital baseband signal and the second gain value.

CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE

This application makes reference to, claims priority to, and claims thebenefit of U.S. Provisional Application Ser. No. 60/868,818, filed onDec. 6, 2006.

This application also makes reference to:

U.S. application Ser. No. 11/618,876 filed on Dec. 31, 2006; and

U.S. application Ser. No. 11/618,864 filed on Dec. 31, 2006.

Each of the above stated applications is hereby incorporated herein byreference in its entirety.

FIELD OF THE INVENTION

Certain embodiments of the invention relate to wireless communications.More specifically, certain embodiments of the invention relate to amethod and system for enhancing efficiency by modulating power amplifiergain.

BACKGROUND OF THE INVENTION

A power amplifier (PA) circuit may be characterized by its mode, or“class” of operation. Exemplary classes include Class A, Class AB, andClass B. In Class A operation, a PA may operate in a conducting, or ON,state during 100% of the cycle, or the entire cycle, of the inputsignal. In Class A operation, the output signal from the PA is typicallya scaled version of the input signal, where the scaling factor is afunction of the gain associated with the PA circuit. However, for ClassA operation, the PA is typically in a conducting state even when thereis no input signal. Furthermore, even when the PA is amplifying an inputsignal, the efficiency of the PA may not exceed 50%.

In Class B operation, a PA may operate in a conducting state during 50%,or half, of the cycle of the input signal. This may result in largeamounts of distortion of the input signal in the output signal. Thehigher efficiency of the Class B PA results from the PA being in anon-conducting, or OFF, state half of the time.

In Class AB operation, a PA may operate in a conducting state forgreater than 50%, but less than 100%, of the cycle of the input signal.In Class AB operation, the PA may be more efficient than in Class Aoperation, but less efficient than in Class B operation. Furthermore, inClass AB operation, the PA may produce more distortion than in Class Aoperation, but less than in Class B operation.

When the peak input signal level to a PA circuit is large compared tothe average input signal level, or high peak to average ratio, the PAcircuit may be biased to accommodate the peak input signal level,P_(INMAX). The value of P_(DC) may be set to enable generation of an RFsignal output level from the PA circuit, P_(RFMAX), when thecorresponding input signal level is P_(INMAX). Thus, efficiency of thePA circuit may be highest for a given value P_(DC) when the RF signaloutput level from the PA circuit is P_(RFMAX). However, for high peak toaverage ratios, the input signal level is typically less than P_(INMAX)for a substantial portion of the time that the PA circuit is operating.Therefore, the average RF signal output level, P_(RFAVG), may besignificantly lower than P_(RFMAX). Consequently, the need to supporthigh peak to average ratios may result in low efficiency for the PAcircuit.

Further limitations and disadvantages of conventional and traditionalapproaches will become apparent to one of skill in the art, throughcomparison of such systems with some aspects of the present invention asset forth in the remainder of the present application with reference tothe drawings.

BRIEF SUMMARY OF THE INVENTION

A method and system for enhancing efficiency by modulating poweramplifier gain, substantially as shown in and/or described in connectionwith at least one of the figures, as set forth more completely in theclaims.

These and other advantages, aspects and novel features of the presentinvention, as well as details of an illustrated embodiment thereof, willbe more fully understood from the following description and drawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a block diagram illustrating and exemplary mobile terminal,which may be utilized in connection with an embodiment of the invention.

FIG. 2 is an exemplary block diagram illustrating an RF transmitterutilizing power amplifier gain modulation, in accordance with anembodiment of the invention.

FIG. 3 is a diagram of an exemplary power amplifier with programmablegain, in accordance with an embodiment of the invention.

FIG. 4 is a flow chart illustrating exemplary steps for a method andsystem for enhancing efficiency by modulating power amplifier gain, inaccordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Certain embodiments of the invention may be found in a method and systemfor enhancing efficiency by modulating power amplifier gain. Variousembodiments of the invention may enable the amplitude of input signalsto a PA circuit to be controlled within an amplitude range, whichenables the PA to operate in an efficient manner. Efficiency, η, for aPA circuit may be defined as in the following equation:

$\begin{matrix}{\eta = \frac{P_{RF}}{P_{DC}}} & \lbrack 1\rbrack\end{matrix}$where P_(RF) refers to the power level for an RF signal output by a PAcircuit in an RF transmitter, and P_(DC) refers to delivered power froma DC power supply source (such as a battery).

In various embodiments of the invention, a baseband processor maydynamically adjust the gain level of a PA modulator. The PA modulatordigitally applies the dynamically adjustable gain level to a digitalbaseband signal to maintain a constant input signal level at a PAcircuit. The input signal level may be selected to enable efficientoperation of the PA. The baseband processor may also send controlsignals to the PA circuit to dynamically control the gain of the PA toenable generation of an output RF signal that is based on a scaled andRF upconverted analog version of the baseband signal. In this inventionthe input of the PA may be kept large most of the time to have higherefficiency.

The efficiency of a PA circuit may increase with increasing input signalamplitudes. Various embodiments of the invention may enable generationof input RF signals that enable efficient PA operation.

FIG. 1 is a block diagram illustrating and exemplary mobile terminal,which may be utilized in connection with an embodiment of the invention.Referring to FIG. 1, there is shown mobile terminal 120 that maycomprise an RF receiver 123 a, an RF transmitter 123 b, a digitalbaseband processor 129, a processor 125, and a memory 127. In someembodiments of the invention, the RF receiver 123 a, and RF transmitter123 b may be integrated into an RF transceiver 122, for example. Asingle transmit and receive antenna 121 may be communicatively coupledto the RF receiver 123 a and the RF transmitter 123 b. A switch 124, orother device having switching capabilities may be coupled between the RFreceiver 123 a and RF transmitter 123 b, and may be utilized to switchthe antenna 121 between transmit and receive functions.

The RF receiver 123 a may comprise suitable logic, circuitry, and/orcode that may enable processing of received RF signals. The RF receiver123 a may enable receiving RF signals in frequency bands utilized byvarious wireless communication systems, such as GSM and/or CDMA, forexample.

The digital baseband processor 129 may comprise suitable logic,circuitry, and/or code that may enable processing and/or handling ofbaseband signals. In this regard, the digital baseband processor 129 mayprocess or handle signals received from the RF receiver 123 a and/orsignals to be transferred to the RF transmitter 123 b for transmissionvia a wireless communication medium. The digital baseband processor 129may also provide control and/or feedback information to the RF receiver123 a and to the RF transmitter 123 b, based on information from theprocessed signals. The digital baseband processor 129 may communicateinformation and/or data from the processed signals to the processor 125and/or to the memory 127. Moreover, the digital baseband processor 129may receive information from the processor 125 and/or to the memory 127,which may be processed and transferred to the RF transmitter 123 b fortransmission via the wireless communication medium.

The RF transmitter 123 b may comprise suitable logic, circuitry, and/orcode that may enable processing of RF signals for transmission. The RFtransmitter 123 b may enable transmission of RF signals in frequencybands utilized by various wireless communications systems, such as GSMand/or CDMA, for example.

The processor 125 may comprise suitable logic, circuitry, and/or codethat may enable control and/or data processing operations for the mobileterminal 120. The processor 125 may be utilized to control at least aportion of the RF receiver 123 a, the RF transmitter 123 b, the digitalbaseband processor 129, and/or the memory 127. In this regard, theprocessor 125 may generate at least one signal for controllingoperations within the mobile terminal 120.

The memory 127 may comprise suitable logic, circuitry, and/or code thatmay enable storage of data and/or other information utilized by themobile terminal 120. For example, the memory 127 may be utilized forstoring processed data generated by the digital baseband processor 129and/or the processor 125. The memory 127 may also be utilized to storeinformation, such as configuration information, which may be utilized tocontrol the operation of at least one block in the mobile terminal 120.For example, the memory 127 may comprise information necessary toconfigure the RF receiver 123 a to enable receiving RF signals in theappropriate frequency band.

FIG. 2 is an exemplary block diagram illustrating an RF transmitterutilizing power amplifier gain modulation, in accordance with anembodiment of the invention. Referring to FIG. 2, there is shown an RFtransmitter 123 b, a delay block 252, and a baseband processor 240. TheRF transmitter 123 b may comprise a power amplifier (PA) 214, a poweramplifier driver (PAD) 212, an RF programmable gain amplifier (RFPGA)210, a transmitter In-phase signal (I) mixer 208 a, a transmitterQuadrature-phase signal (Q) mixer 208 b, an I transconductance amplifier(gm) 206 a, a Q gm 206 b, an I low pass filter (LPF) 204 a, a Q LPF 204b, an I digital to analog converter (I DAC) 202 a, and a Q DAC 202 b.The baseband processor 240 may comprise a PA gain modulator 242, and asignal modulator 244.

The PA 214 may comprise suitable logic, circuitry, and/or code that mayenable amplification of input signals to generate a transmitted signalof sufficient signal power (as measured by dBm, for example) fortransmission via a wireless communication medium. In an exemplaryembodiment of the invention, the PA 214 may receive a differential inputsignal, labeled PA_(in) in FIG. 2, and output a differential outputsignal, labeled RF_(out) in FIG. 2. In addition, the PA 214 may receivea control signal, labeled Gain Control in FIG. 2, which may enable thePA 214 to dynamically select a gain level, referred to as g₃(t). Thegain level may vary with time in response to the Gain Control signal.The gain level may determine an amplification level by which the inputsignal PA_(in) may be amplified to generate the output signal RF_(out).

The PAD 212 may comprise suitable logic, circuitry, and/or code that mayenable amplification of input signals to generate an amplified outputsignal. The PAD 212 may be utilized in multistage amplifier systemswherein the output of the PAD 212 may be an input to a subsequentamplification stage. In an exemplary embodiment of the invention, thePAD 212 may receive a differential input signal and output adifferential output signal, labeled PA_(in) in FIG. 2.

The RFPGA 210 may comprise suitable logic, circuitry, and/or code thatmay enable amplification of input signals to generate an amplifiedoutput signal, wherein the amount of amplification, as measured in dBfor example, may be determined based on an input control signal. Invarious embodiments of the invention, the input control signal maycomprise binary bits. In an exemplary embodiment of the invention, theRFPGA 210 may receive a differential input signal and generate adifferential output signal.

The transmitter I mixer 208 a may comprise suitable logic, circuitry,and/or code that may enable generation of an RF signal by upconversionof an input signal. The transmitter I mixer 208 a may utilize an inputlocal oscillator signal labeled as LO_(208a) to upconvert the inputsignal. The upconverted signal may be an RF signal. The transmitter Imixer 208 a may produce an RF signal for which the carrier frequency maybe equal to the frequency of the signal LO_(208a). In an exemplaryembodiment of the invention, the transmitter I mixer 208 a may receive adifferential input signal and generate a differential output signal.

The transmitter Q mixer 208 b may be substantially similar to thetransmitter I mixer 208 a. The transmitter Q mixer 208 b may utilize aninput local oscillator signal labeled as LO_(208b) in quadrature (inFIG. 2) to upconvert the input signal.

The I gm 206 a may comprise suitable, logic, circuitry, and/or code thatmay enable generation of an output current, the amplitude of which maybe proportional to an amplitude of an input voltage, wherein the measureof proportionality may be determined based on the transconductanceparameter, gm_(I), associated with the I gm 206 a. In an exemplaryembodiment of the invention, the I gm 206 a may receive a differentialinput signal and output a differential output signal.

The Q gm 206 b may be substantially similar to the I gm 206 a. Thetransconductance parameter associated with the Q gm 206 b is gm_(Q).

The I LPF 204 a may comprise suitable logic, circuitry, and/or code thatmay enable selection of a cutoff frequency, wherein the LPF mayattenuate the amplitudes of input signal components for which thecorresponding frequency is higher than the cutoff frequency, while theamplitudes of input signal components for which the correspondingfrequency is less than the cutoff frequency may “pass,” or not beattenuated, or attenuated to a lesser degree than input signalcomponents at frequencies higher than the cutoff frequency. In variousembodiments of the invention, the I LPF 210 a may be implemented as apassive filter, such as one that utilizes resistor, capacitor, and/orinductor elements, or implemented as an active filter, such as one thatutilizes an operational amplifier. In an exemplary embodiment of theinvention, the I LPF 210 a may receive a differential input signal andoutput a differential output signal.

The Q LPF 204 b may be substantially similar to the I LPF 204 a.

The I DAC 202 a may comprise suitable logic, circuitry, and/or code thatmay enable conversion of an input digital signal to a correspondinganalog representation.

The Q DAC 202 b may be substantially similar to the I DAC 202 a.

The baseband processor 240 may comprise suitable logic, circuitry,and/or code that may enable processing tasks, which correspond to one ormore layers in an applicable protocol reference model (PRM). Forexample, the baseband processor 240 may perform physical (PHY) layerprocessing, layer 1 (L1) processing, medium access control (MAC) layerprocessing, logical link control (LLC) layer processing, layer 2 (L2)processing, and/or higher layer protocol processing. The processingtasks performed by the baseband processor 240 may be referred to asbeing within the digital domain. The baseband processor 240 may alsogenerate control signals. In an exemplary embodiment of the invention,the baseband processor 240 may generate differential output signals. Thedifferential output signals may be referred to as quadrature basebandsignals labeled I_(BB) and Q_(BB) in FIG. 2.

The signal modulator 244 may comprise suitable logic, circuitry and/orcode that may enable generation of modulated baseband signals, labeledSIG_(BB) in FIG. 2. The modulated baseband signals may be digitalsignals generated based on binary data. The amplitude of the signalsSIG_(BB) may vary with time. In an exemplary embodiment of theinvention, the amplitude of the signals SIG_(BB) may vary over a rangefrom −50 dBm to 10 dBm.

The PA gain modulator 242 may comprise suitable logic, circuitry and/orcode that may enable generation of quadrature baseband signals, labeledI_(BB) and Q_(BB) in FIG. 2, from a received modulated baseband signal,labeled SIG_(BB) in FIG. 2. The PA gain modulator 242 may utilize thereceived modulated baseband signal, for which the amplitude may varywith time, to generate an intermediate signal, INT_(BB), for which theamplitude is constant with time. The PA gain modulator 242 may utilizethe intermediate signal to generate the quadrature baseband signalsI_(BB) and Q_(BB).

The PA gain modulator 242 may determine a dynamic gain level, g₁(t),when generating the signal INT_(BB) from the signal SIG_(BB) such that:∥INT _(BB)(t)∥=g ₁(t)·∥SIG _(BB)(t)∥  [2]and:∥INT _(BB)(t)∥=Constant  [3]where t represents time, ∥INT_(BB)(t)∥ represents the non-time varyingamplitude of the intermediate signal, ∥SIG_(BB)(t)∥ represents the timevarying amplitude of the modulated baseband signal, and Constantrepresents a numerical constant. Based on the dynamic gain level, g₁(t),the PA gain modulator 242 may generate control signals, labeled ControlSignals in FIG. 2.

In various embodiments of the invention, the dynamic gain level, g₁(t),may be utilized to compute the intermediate signal by digitalprocessing. For example the digital SIG_(BB) signal may be utilized asan input to a lookup table (LUT) which may generate a digital INT_(BB)signal for a given gain level g₁(t).

The delay block 252 may comprise suitable logic, circuitry and/or codethat may enable reception of an input signal, labeled Control Signals inFIG. 2, and generation of output signals, labeled Gain Control in FIG.2. The delay block 252 may receive the Control Signals at a time instantt₀, and then output the Control Signals at a later time instant t₁ asGain Control signals.

In operation, the baseband processor 240 may generate data comprising asequence of bits to be transmitted via a wireless communication medium.The signal modulator 244 may utilize the generated sequence of bits togenerate a baseband signal SIG_(BB). The amplitude of the basebandsignal, ∥SIG_(BB)(t)∥, may vary with time. The PA gain modulator 242 mayreceive the baseband signal SIG_(BB) and generate an intermediatesignal, INT_(BB). The amplitude of the intermediate signal ∥INT_(BB)(t)∥may be constant. The baseband processor 240 may configure the PA gainmodulator 242 to select a value for the constant amplitude level,Constant, as set forth in equation [3]. A dynamic gain level g₁(t) maybe computed as set forth in equation [2]. Based on the computed dynamicgain level g₁(t), the PA gain modulator 242 may generate controlsignals, labeled Control Signals in FIG. 2, which may be sent to thedelay block 252.

Based on the intermediate signal, the baseband processor 240 maygenerate quadrature baseband signals labeled I_(BB) and Q_(BB) in FIG.2. The baseband processor 240 may send the I_(BB) signal to the I DAC202 a, and send the Q_(BB) signal to the Q DAC 202 b. The I DAC 202 amay generate an analog signal. The Q DAC 202 b may similarly generate ananalog signal.

The analog signals generated by the I DAC 202 a and Q DAC 202 b maycomprise undesirable frequency components. The I LPF 204 a and Q LPF 204b may attenuate signal amplitudes associated with these undesirablefrequency components in signals generated by the I DAC 202 a and Q DAC202 b respectively. The baseband processor 240 may configure thetransmitter I mixer 208 a to select a frequency for the LO_(208a) signalutilized to upconvert the filtered signal from the I LPF 204 a. Theupconverted signal output from the transmitter I mixer 208 a maycomprise an I component RF signal. The baseband processor 240 maysimilarly configure the transmitter Q mixer 208 b to generate a Qcomponent RF signal from the filtered signal from the Q LPF 204 b.

The RFPGA 210 may amplify the I component and Q component RF signals togenerate an RF signal, wherein the level of amplification that may beprovided by the RFPGA 210 may be configured based on control signalsgenerated by the baseband processor 240. The PAD 212 may provide asecond stage of amplification for the signal generated by the RFPGA 210.The PAD 212 may generate an input RF signal to the PA 214, labeledPA_(in) in FIG. 2. The level of signal gain in the RF transmitter 123 bfrom the signal INT_(BB) to the signal PA_(in) may be referred to as g₂.In various embodiments of the invention, g₂ may be as in the followingequation:g₂=c₁  [4]where c₁ is a numerical constant.

The delay block 252 may utilize the previously received Control Signalsfrom the PA gain modulator 242 to generate a Gain Control signal. Thedelay block 252 may delay generation of the Gain Control signal from thereceived Control Signal by a suitable amount of time so as to apply theGain Control signal to a PA_(in) signal that was generated in responseto the previous I_(BB) and Q_(BB) signals. The PA 214 may receive theGain Control signal and dynamically select an amplification level,g₃(t), which may be utilized to generate an output RF signal, RF_(out),such that:∥RF _(out)(t)∥=g ₃(t)·∥PA _(in)(t)∥  [5]where ∥RF_(out)(t)∥ refers to the amplitude of the PA 214 output signal,and ∥PA_(in)(t)∥ refers to the amplitude of the PA 214 input signal. Invarious embodiments of the invention, the amplitude ∥PA_(in)(t)∥ may beconstant with time. The PA output signal may be related to the basebandinput signal as shown in the following equation:∥RF _(out)(t)∥=G·∥SIG _(BB)(t)∥  [6]where G represents an overall gain level through the baseband processor240 and RF transmitter 123 b. The value for G may be as shown in thefollowing equation:G=g ₁(t)·g ₂ ·g ₃(t)  [7]where g₁(t) is as described in equation [2], g₂ is as described inequation [4], and g₃(t) is as described in equation [5]. In variousembodiments of the invention, G may be as shown in the followingequation:G=c₂  [8]where c₂ is a numerical constant.

The amplified signal from the PA 214, RF_(out), may be transmitted tothe wireless communications medium via the antenna 121.

In various embodiments of the invention, the PA gain modulator 242 maycompute a value g₁(t) in accordance with equation [2] at a given timeinstant. Based on the computed value g₁(t), a value g₃(t) may becomputed in accordance with equations [4], [7], and [8]. The PA gainmodulator 242 may generate Control Signals based on the computed valueg₃(t). The delay block 252 may generate corresponding Gain Controlsignals that enable the PA 214 to be configured to provide a g₃(t) levelof signal amplification.

In an exemplary embodiment of the invention, an increase in theamplitude ∥SIG_(BB)(t)∥ may result in a decrease in the gain level g₁(t)and a corresponding increase in the gain level g₃(t) in accordance withequations [4], [7] and [8]. The decrease in the gain level g₁(t) may,for example, enable the amplitude ∥PA_(in)(t)∥ to remain constant evenwhen there is an increase in the amplitude ∥SIG_(BB)(t)∥. The increasein the gain level g₃(t) may enable the overall gain level between thesignal SIG_(BB) and the signal RF_(out) to remain constant at a level c₂(as set forth in equation [8] above) even when the respectiveintermediate gain levels g₁(t) and g₃(t) are dynamically adjusted. Forexample, when ∥SIG_(BB)(t)∥ decreases, the gain g₁(t) increases, and thegain g₃(t) decreases such that ∥PA_(in)(t)∥ remains constant. In variousembodiments of the invention, the increase in g₁(t) and decrease ing₃(t) are in accordance with equations [4], [7] and [8]. The value of∥PA_(in)(t)∥ may be selected to enable the PA 214 to operate with highefficiency. Thus, in various embodiments of the invention, the peak toaverage ratio at the PA may be reduced in comparison to systems, whichdo not dynamically adjust PA gain levels.

FIG. 3 is a diagram of an exemplary power amplifier with programmablegain, in accordance with an embodiment of the invention. Referring toFIG. 3, there is shown a PA 214. The PA 214 may comprise a plurality ofinductors 302 and 304, and a plurality of gain stages 310, . . . , and320. The gain stage 310 may comprise a plurality of transistors 312,314, 316 and 318. The gain stage 320 may comprise a plurality oftransistors 322, 324, 326 and 328.

The plurality of gain stages 310, . . . , and 320 may compriseindividually selectable gain stages that may be enabled to dynamicallyincrease gain, g₃(t) for the PA 214, or disabled to dynamically decreasePA 214 gain g₃(t). Individual gain stages may be selected based on thesignal labeled Gain Control in FIG. 2. The gain stage 310 may representa first gain stage in the plurality of gain stages, and the gain stage320 may represent a last gain stage in a plurality of n gain stages.

The gain stage 310 may receive a control signals, labeled Ctl_(s1−) inFIG. 3, which enables or disables the gain stage 310. When enabled, thegain stage 310 may provide a g_(s1) level of amplification of thedifferential input signal to transistors 316 and 318, labeled asPA_(in+) and PA_(in−) respectively in FIG. 3. The first stage gainlevel, g_(s1), may contribute to the overall level of gain in the PA214, g₃(t).

The gain stage 320 may receive a control signal, labeled Ctl_(sn) inFIG. 3, which enables or disables the gain stage 320. When enabled, thegain stage 320 may provide a g_(sn) level of amplification of thedifferential input signal to transistors 326 and 328, labeled asPA_(in+) and PA_(in−) respectively in FIG. 3. The n^(th) stage gainlevel, g_(sn), may contribute to the overall level of gain in the PA214, g₃(t).

The overall level of gain, g₃(t), for the PA 214 may be collectivelybased on the individual stage gains, g_(si), for each of the enabledgain stages i.

FIG. 4 is a flow chart illustrating exemplary steps for a method andsystem for enhancing efficiency by modulating power amplifier gain, inaccordance with an embodiment of the invention. Referring to FIG. 4, instep 402 the baseband processor 240 may select a constant amplitude,Constant, for the intermediate signal INT_(BB), as shown in equation[3], which corresponds to the maximum desirable PA input level to havethe maximum efficiency in the PA. In step 404, a baseband signal,SIG_(BB), may be generated by the signal modulator 244. In step 406, thePA gain modulator 242 may compute the gain level, g₁(t), in accordancewith equation [2]. The PA gain modulator 242 may also compute a gainlevel, g₃(t), in accordance with equations [4], [7] and [8], andgenerate Control Signals (FIG. 2).

In step 408, the baseband processor 240 may generate quadrature basebandsignals, I_(BB) and Q_(BB), based on the intermediate signal INT_(BB).In step 410, the PAD 212 may generate an RF input signal to the PA 214,PA_(in). In step 412, the PA 214 may receive Gain Control signals (FIG.2) based on the Control Signals (FIG. 2) that enable the PA 214 to beconfigured to provide a gain level, g₃(t) for amplification of thePA_(in) signal. In step 414, the PA 214 may generate an output signal,RF_(out). Step 404 may follow step 414 as the baseband processor 240generates a subsequent baseband signal.

In an exemplary embodiment of the invention, the value c₂ (equation [8])may be 50 dB, and the value c₁ (equation [4]) may be 40 dB. For anexemplary baseband signal for which ∥SIG_(BB)(t)∥=0 dB, exemplary valuesg₁(t)=10 dB, g₂=40 dB, and g₃(t)=0 dB may be utilized. In this case,∥PA_(in)(t)∥=50 dB and ∥RF_(out)(t)∥=50 dB. For an exemplary basebandsignal for which ∥SIG_(BB)(t)∥=10 dB, exemplary values g₁(t)=0 dB, g₂=40dB, and g₃(t)=10 dB may be utilized. In this case, ∥PA_(in)(t)∥=50 dBand ∥RF_(out)(t)∥=60 dB. In each exemplary case the amplitude of theinput signal to the PA 214 is 50 dB. In an exemplary embodiment of theinvention, the amplitude level ∥PA_(in)(t)∥=50 dB may enable efficientoperation of the PA 214 circuit. RF_(out) is the amplified version ofSIG_(BB) with the same variation, however the input of the PA is alwaysconstant to have the maximum efficiency in the PA.

Aspects of a method and system for enhancing efficiency by modulatingpower amplifier (PA) gain may comprise a PA gain modulator 242 thatenables modification of an amplitude of a digital baseband signal. Abaseband processor 240 may enable computation of a first gain value,g₁(t) based on the modification. The baseband processor 240 may enablecomputation of a second gain, g₃(t), value based on the first gainvalue. A PA 214 may enable generation of an RF output signal based onthe modified digital baseband signal and the second gain value. Themultiplicative product of the first gain value and the second gain valuemay be a constant value. The amplitude of the digital baseband signalmay be time varying. The amplitude of the modified digital basebandsignal may be constant.

The baseband processor 240 may enable generation of quadrature basebandsignals based on the modified digital baseband signal. The PAD 212 mayenable generation of an input RF signal based on the generatedquadrature baseband signals. At least a portion of the RF transmitter123 b chain may enable generation of the input RF signal based on themodified digital baseband signal and a third gain value, g₂. The thirdgain value may be a constant value. The PA 214 may enable generation ofthe RF output signal based on the generated input RF signal and thesecond gain value. The amplitude of the input RF signal may be constant.

In various embodiments of the invention, AM-AM distortion and/or AM-PMdistortion that may result from dynamic gain adjustment may be reducedby utilizing a calibration feedback and input predistortion method as isdescribed in U.S. patent application Ser. No. 11/618,876, which isincorporated herein by reference in its entirety.

Accordingly, the present invention may be realized in hardware,software, or a combination of hardware and software. The presentinvention may be realized in a centralized fashion in at least onecomputer system, or in a distributed fashion where different elementsare spread across several interconnected computer systems. Any kind ofcomputer system or other apparatus adapted for carrying out the methodsdescribed herein is suited. A typical combination of hardware andsoftware may be a general-purpose computer system with a computerprogram that, when being loaded and executed, controls the computersystem such that it carries out the methods described herein.

The present invention may also be embedded in a computer programproduct, which comprises all the features enabling the implementation ofthe methods described herein, and which when loaded in a computer systemis able to carry out these methods. Computer program in the presentcontext means any expression, in any language, code or notation, of aset of instructions intended to cause a system having an informationprocessing capability to perform a particular function either directlyor after either or both of the following: a) conversion to anotherlanguage, code or notation; b) reproduction in a different materialform.

While the present invention has been described with reference to certainembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the scope of the present invention. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the present invention without departing from its scope.Therefore, it is intended that the present invention not be limited tothe particular embodiment disclosed, but that the present invention willinclude all embodiments falling within the scope of the appended claims.

1. A method for controlling gain in an amplifier circuit, the methodcomprising: modifying an amplitude of a digital baseband signal;computing a first gain value based on said modifying; computing a secondgain value based on said first gain value; and generating an RF outputsignal based on said modified digital baseband signal and said secondgain value.
 2. The method according to claim 1, wherein a multiplicativeproduct of said first gain value and said second gain value is aconstant value.
 3. The method according to claim 1, wherein saidamplitude of said digital baseband signal is time varying.
 4. The methodaccording to claim 1, wherein an amplitude of said modified digitalbaseband signal is constant.
 5. The method according to claim 1,comprising generating quadrature baseband signals based on said modifieddigital baseband signal.
 6. The method according to claim 5, comprisinggenerating an input RF signal based on said generated quadraturebaseband signals.
 7. The method according to claim 6, comprisinggenerating said input RF signal based on said modified digital basebandsignal and a third gain value.
 8. The method according to claim 7,wherein said third gain value is a constant value.
 9. The methodaccording to claim 6, comprising generating said generated RF outputsignal based on said generated input RF signal and said second gainvalue.
 10. The method according to claim 9, wherein an amplitude of saidgenerated input RF signal is constant.
 11. The method according to claim1, comprising dynamically adjusting said first gain value based on saidamplitude of said digital baseband signal.
 12. The method according toclaim 11, comprising dynamically adjusting said second gain value inresponse to said dynamically adjusted said first gain value.
 13. Themethod according to claim 12, wherein a multiplicative product of saidfirst gain value and said second gain value is approximately equal to amultiplicative product of said dynamically adjusted said first gainvalue and said dynamically adjusted said second gain value.
 14. A systemfor controlling gain in an amplifier circuit, the system comprising: oneor more circuits that are operable to modify an amplitude of a digitalbaseband signal; said one or more circuits are operable to compute afirst gain value based on said modification; said one or more circuitsare operable to compute a second gain value based on said first gainvalue; and said one or more circuits are operable to generate an RFoutput signal based on said modified digital baseband signal and saidsecond gain value.
 15. The system according to claim 14, wherein amultiplicative product of said first gain value and said second gainvalue is a constant value.
 16. The system according to claim 14, whereinsaid amplitude of said digital baseband signal is time varying.
 17. Thesystem according to claim 14, wherein an amplitude of said modifieddigital baseband signal is constant.
 18. The system according to claim14, wherein said one or more circuits are operable to generatequadrature baseband signals based on said modified digital basebandsignal.
 19. The system according to claim 18, wherein said one or morecircuits are operable to generate an input RF signal based on saidgenerated quadrature baseband signals.
 20. The system according to claim19, wherein said one or more circuits are operable to generate saidinput RF signal based on said modified digital baseband signal and athird gain value.
 21. The system according to claim 20, wherein saidthird gain value is a constant value.
 22. The system according to claim19, wherein said one or more circuits are operable to generate saidgenerated RF output signal based on said generated input RF signal andsaid second gain value.
 23. The system according to claim 22, wherein anamplitude of said generated input RF signal is constant.
 24. The systemaccording to claim 23, wherein said one or more circuits are operable todynamically adjust said first gain value based on a said amplitude ofsaid digital baseband signal.
 25. The system according to claim 24,wherein said one or more circuits are operable to dynamically adjustsaid second gain value in response to said dynamically adjusted saidfirst gain value.
 26. The system according to claim 25, wherein amultiplicative product of said first gain value and said second gainvalue is approximately equal to a multiplicative product of saiddynamically adjusted said first gain value and said dynamically adjustedsaid second gain value.